D. The patient has chronic HBV infection.
HBsAg enzyme immunoassay is the first serologic marker to appear in serum at 1 to 10 weeks after infection with HBV and 2 to 8 weeks before the onset of clinical symptoms of hepatitis B.1,2 After acute infection, HBsAg typically disappears 1 to 3 months after symptom onset.1,2 Persistence of HBsAg for more than 6 months, consistent with chronic HBV, is the primary indicator of risk for developing chronic liver disease and hepatocellular carcinoma later in life.1 Thus, HBsAg can assist with diagnosing both acute and chronic hepatitis B.1,2 A negative HBsAg test result rules out acute hepatitis B infection, except during the “window period,” which is the time typically between 100 and 160 days after symptom onset when HBsAg disappears and before anti-HBs appear.1,2 During this time, the total and IgM hepatitis B core antibodies (anti-HBc) are the only serologic markers present.1,2 In the setting of chronic hepatitis B, the absence of HBsAg can occur in the setting of variants in the surface S gene (S-escape variants), evading detection by HBsAg assays and consistent with occult chronic hepatitis B.1,3,4 The prevalence of occult chronic hepatitis B is approximately 0.11% in highly endemic areas.5